The only reason i can come up here is that the sensor is built by a company that until now doesn't have the reputation to build good sensors and if that is the case, it might have been in Oly's interst to keep silence to avoid discussions.

This is the only plausible explanation I have heard. If this was a Samsung sensor made to Olympus specifications, it would likely be better for Olympus to keep the Samsung name out of the marketing material. Samsung sensors are doing Ok, even at 20 megapixel, but the public perception might be different.

. . . Well since we're all just guessing here, I think that there's an upcoming announcement coming later this month about Olympus entering in to an alliance with Sony and that Sony might have sweetened their offer by selling to Olympus a sensor for the OM-D.

While we're into guessing, my guess is that someone at the Olympus labs found themselves with an oversupply of face cream, and made the chance discovery that applying it to a Panasonic sensor enhanced its working
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Bob